应该是BACKLIGHT的问题

Backlight is essentially an inverter + cathode tubes. If the screen is completely dark, get a bright flashlight, project the light on the screen and see if there is still a picture. If you can still see the picture, it's definitely the backlight. Most likely you need to replace the inverter alone with the cathode tubes. It cost ~20USB, but to find the exact size tube that fits your monitor can be a challenge.

If inventer is overheating, it may cause flickering of the cathode tubes. Maybe you can add a PC case fan somethere to cool it down.